This application claims benefit of Japanese Application No. 2000-239630 filed in Japan on Aug. 8, 2000, the contents of which are incorporated by this reference.
1. Field of the Invention
The present invention relates to image display apparatus having a three-dimensionally decentered optical path. More particularly, the present invention relates to a head- or face-mounted image display apparatus that can be retained on an observer""s head or face and allows observation of the image of a single image display device with two eyes.
2. Discussion of Related Art
Image display apparatus designed to observe the image of a single image display device with two eyes have heretofore been known in Japanese Patent Application Unexamined Publication Nos. [hereinafter referred to as xe2x80x9cJP(A)xe2x80x9d] 6-110013, 7-287185, 9-61748, 9-181998, and 9-181999, Published Japanese Translation of PCT International Publication No. Hei 10-504115, etc.
Among them, the image display apparatus of JP(A) 6-110013 splits and folds light rays by using a prism in the shape of an isosceles triangular prism and a mirror. Therefore, correction of various aberrations is performed by using a lens placed in front of the pupil. This makes it difficult to correct aberrations, and at the same time, causes the apparatus to become large in size. JP(A) 7-287185 uses a plurality of mirrors and performs image formation with a single convex lens. Therefore, it is very difficult to perform assembly adjustment. In addition, appropriate performance cannot be attained. Although the image display device is placed three dimensionally, the optical systems for the left and right eyes are in bilateral symmetry with each other. Therefore, the images of the image display device that are displayed in the left and right eyes are in oppositely rotated relation to each other.
In JP(A) 9-61748, display light from an LCD (Liquid Crystal Display) is split by using a half-mirror so as to be observed with two eyes. Because the display light is distributed to the left and right eyeballs, the image for observation is weak in light intensity and hence dark. In JP(A) 9-181998 and 9-181999, optical paths for two eyes are provided sidewardly of the image display device. Therefore, the tilt angle of the principal rays with respect to the image display device is very large. Accordingly, these apparatus cannot use an ordinary LCD (Liquid Crystal Display) because the viewing angle thereof is not sufficiently wide.
The image display apparatus of Published Japanese Translation of PCT International Publication No. Hei 10-504115 splits display light by using a half-mirror. The image display apparatus has a very large number of components and requires a very complicated assembling operation.
Recently, with the achievement of small-sized image display devices, it has become necessary to reduce the focal length of the viewing optical system in order to ensure the same field angle. However, if the focal length is shortened, it becomes difficult to ensure the required back focus, and it becomes impossible to increase the optical path length within the prism. As a result, it becomes impossible to increase the number of reflecting surfaces and hence impossible to correct decentration aberrations satisfactorily.
Further, with the recent development of manufacturing techniques, image display devices are becoming higher in definition year by year.
The present invention was made in view of the above-described problems with the prior art.
Accordingly, an object of the present invention is to provide an image display apparatus, e.g. a head-mounted image display apparatus, in which an image from a single image display device is led to two eyes without using a half-mirror, thereby allowing observation of a bright image, and in which at least three curved reflecting surfaces are used to form an optical system, thereby allowing correction of various aberrations in conformity to recent compact and high-definition image display devices.
Another object of the present invention is to provide an image display apparatus favorably improved in terms of the tilt angle of the principal rays with respect to the image display device.
To attain the above-described objects, the present invention provides an image display apparatus having a three-dimensionally decentered optical path. The image display apparatus includes an image display device for forming an image for observation on an image display area. The image display apparatus further includes a viewing optical system for leading the image formed by the image display device to a pupil corresponding to a position where an eyeball of an observer is to be placed.
The image display device is a single image display device having a plurality of pixels juxtaposed on a single substrate.
Each pixel located at least in the central portion of the single image display device is arranged to emit an image light beam at such an exit angle that the light beam can be led to the left and right eyes of the observer.
The viewing optical system includes at least a left ocular part for leading the light beam to the left eye of the observer; a right ocular part for leading the light beam to the right eye of the observer; and an optical path distributing part for distributing the image light beam emitted from the image display device at the above-described exit angle to the left and right ocular parts.
The left ocular part has at least two reflecting surfaces. At least one of the at least two reflecting surfaces is formed from a rotationally asymmetric curved reflecting surface having the function of correcting decentration aberrations.
The right ocular part has at least two reflecting surfaces. At least one of the at least two reflecting surfaces is formed from a rotationally asymmetric curved reflecting surface having the function of correcting decentration aberrations.
The optical path distributing part has at least one pair of reflecting surfaces for left and right optical paths for the left and right eyes of the observer. The reflecting surfaces are each formed from a rotationally asymmetric curved reflecting surface having the function of correcting decentration aberrations.
The left and right optical paths of the viewing optical system are formed by optical surfaces arranged so that the left and right optical paths are not in plane symmetry with each other but in 180-degree rotational symmetry with respect to only a normal line passing through the center of the image display device.
The reasons for adopting the above-described arrangement in the present invention, together with the function thereof, will be described below.
FIG. 1 shows the left and right optical paths (for the left and right eyes) and optical surfaces of the viewing optical system in the image display apparatus according to Example 1 (described later). Part (a) of FIG. 1 is a plan view. Part (b) of FIG. 1 is a side view. In the figure, L and R are suffixed to reference symbols to distinguish between the left and right optical surfaces, axial principal rays and pupils. The reference symbols are put to the constituent elements in the order of backward ray tracing to match with the description of numerical data (shown later).
The viewing optical system includes a left ocular part 10L for leading a light beam to an observer""s left eye positioned at a left pupil 1L and a right ocular part 10R for leading a light beam to an observer""s right eye positioned at a right pupil 1R. The viewing optical system further includes an optical path distributing part (optical path distributing prism in Example 1, which is shown in FIG. 1) 20 for leading an image light beam emitted from an image display device 3 at a predetermined exit angle to the left and right ocular parts 10L and 10R.
The left and right ocular parts 10L and 10R each have at least two reflecting surfaces (back-coated mirrors 12L and 12R and totally reflecting surfaces 13L and 13R in the case of FIG. 1). At least one of the at least two reflecting surfaces is formed from a rotationally asymmetric curved reflecting surface having the function of correcting decentration aberrations.
In the present invention, a free-form surface is used as a typical example of a surface having a rotationally asymmetric curved surface configuration. A free-form surface is defined by the following equation. The Z-axis of the defining equation is the axis of a free-form surface.                     Z        =                              c            ⁢                          xe2x80x83                        ⁢                                          r                2                            /                              [                                  1                  +                                                            {                                              1                        -                                                                              (                                                          1                              +                              k                                                        )                                                    ⁢                                                      c                            2                                                    ⁢                                                      r                            2                                                                                              }                                                                      ]                                              +                                    ∑                              j                =                2                            66                        ⁢                                          C                j                            ⁢                              X                m                            ⁢                              Y                n                                                                        (        a        )            
In the equation (a), the first term is a spherical surface term, and the second term is a free-form surface term.
In the spherical surface term:
c: the curvature at the vertex
k: a conic constant
r={square root over ( )}(X2+Y2)
The free-form surface term is given by
            ∑              j        =        2            66        ⁢                  C        j            ⁢              X        m            ⁢              Y        n              =                    C        2            ⁢      X        +                  C        3            ⁢      Y        +                  C        4            ⁢              X        2              +                  C        5            ⁢      X      ⁢              xe2x80x83            ⁢      Y        +                  C        6            ⁢              Y        2              +                  C        7            ⁢              X        3              +                  C        8            ⁢              X        2            ⁢      Y        +                  C        9            ⁢      X      ⁢              xe2x80x83            ⁢              Y        2              +                  C        10            ⁢              Y        3              +                  C        11            ⁢              X        4              +                  C        12            ⁢              X        3            ⁢      Y        +                  C        13            ⁢              X        2            ⁢              Y        2              +                  C        14            ⁢      X      ⁢              xe2x80x83            ⁢              Y        3              +                  C        15            ⁢              Y        4              +                  C        16            ⁢              X        5              +                  C        17            ⁢              X        4            ⁢      Y        +                  C        18            ⁢              X        3            ⁢              Y        2              +                  C        19            ⁢              X        2            ⁢              Y        3              +                  C        20            ⁢      X      ⁢              xe2x80x83            ⁢              Y        4              +                  C        21            ⁢              Y        5              +                  C        22            ⁢              X        6              +                  C        23            ⁢              X        5            ⁢      Y        +                  C        24            ⁢              X        4            ⁢              Y        2              +                  C        25            ⁢              X        3            ⁢              Y        3              +                  C        26            ⁢              X        2            ⁢              Y        4              +                  C        27            ⁢              XY        5              +                  C        28            ⁢              Y        6              +                  C        29            ⁢              Y        7              +                  C        30            ⁢              X        6            ⁢      Y        +                  C        31            ⁢              X        5            ⁢              Y        2              +                  C        32            ⁢              X        4            ⁢              Y        3              +                  C        33            ⁢              X        3            ⁢              Y        4              +                  C        34            ⁢              X        2            ⁢              Y        5              +                  C        35            ⁢              XY        6              +                  C        36            ⁢              Y        7            
where Cj (j is an integer of 2 or higher) are coefficients.
In general, the above-described free-form surface does not have planes of symmetry in both the XZ- and YZ-planes. However, a free-form surface having only one plane of symmetry parallel to the YZ-plane is obtained by making all terms of odd-numbered degrees with respect to X zero. A free-form surface having only one plane of symmetry parallel to the XZ-plane is obtained by making all terms of odd-numbered degrees with respect to Y zero.
In addition, free-form surfaces as the above-described surfaces with a rotationally asymmetric curved surface configuration may be defined by Zernike polynomials. That is, the configuration of a free-form surface may be defined by the following equation (b). The Z-axis of the defining equation (b) is the axis of Zernike polynomial. A rotationally asymmetric surface is defined by polar coordinates of the height of the Z-axis with respect to the XY-plane. In the equation (b), R is the distance from the Z-axis in the XY-plane, and A is the azimuth angle about the Z-axis, which is expressed by the angle of rotation measured from the X-axis.
x=Rxc3x97cos (A)
y=Rxc3x97sin (A)                                                         Z              =                              xe2x80x83                            ⁢                                                D                  2                                +                                                      D                    3                                    ⁢                  R                  ⁢                                      xe2x80x83                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                    A                    )                                                  +                                                      D                    4                                    ⁢                  R                  ⁢                                      xe2x80x83                                    ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                                      (                    A                    )                                                  +                                                      D                    5                                    ⁢                                      R                    2                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          2                      ⁢                      A                                        )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    D                    6                                    ⁡                                      (                                                                  R                        2                                            -                      1                                        )                                                  +                                                      D                    7                                    ⁢                                      R                    2                                    ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          2                      ⁢                      A                                        )                                                  +                                                      D                    8                                    ⁢                                      R                    3                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          3                      ⁢                      A                                        )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      9                                        ⁡                                          (                                                                        3                          ⁢                                                      R                            3                                                                          -                                                  2                          ⁢                          R                                                                    )                                                        ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                    A                    )                                                  +                                                                            D                      10                                        ⁡                                          (                                                                        3                          ⁢                                                      R                            3                                                                          -                                                  2                          ⁢                          R                                                                    )                                                        ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                                      (                    A                    )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    D                    11                                    ⁢                                      R                    3                                    ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          3                      ⁢                      A                                        )                                                  +                                                      D                    12                                    ⁢                                      R                    4                                    ⁢                                      cos                    ⁡                                          (                                              4                        ⁢                        A                                            )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      13                                        ⁡                                          (                                                                        4                          ⁢                                                      R                            4                                                                          -                                                  3                          ⁢                                                      R                            2                                                                                              )                                                        ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          2                      ⁢                      A                                        )                                                  +                                                      D                    14                                    ⁡                                      (                                                                  6                        ⁢                                                  R                          4                                                                    -                                              6                        ⁢                                                  R                          2                                                                    +                      1                                        )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      15                                        ⁡                                          (                                                                        4                          ⁢                                                      R                            4                                                                          -                                                  3                          ⁢                                                      R                            2                                                                                              )                                                        ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          2                      ⁢                      A                                        )                                                  +                                                      D                    16                                    ⁢                                      R                    4                                    ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          4                      ⁢                      A                                        )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    D                    17                                    ⁢                                      R                    5                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          5                      ⁢                      A                                        )                                                  +                                                                            D                      18                                        ⁡                                          (                                                                        5                          ⁢                                                      R                            5                                                                          -                                                  4                          ⁢                                                      R                            3                                                                                              )                                                        ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          3                      ⁢                      A                                        )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      19                                        ⁡                                          (                                                                        10                          ⁢                                                      R                            5                                                                          -                                                  12                          ⁢                                                      R                            3                                                                          +                                                  3                          ⁢                          R                                                                    )                                                        ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                    A                    )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      20                                        ⁡                                          (                                                                        10                          ⁢                                                      R                            5                                                                          -                                                  12                          ⁢                                                      R                            3                                                                          +                                                  3                          ⁢                          R                                                                    )                                                        ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                                      (                    A                    )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      21                                        ⁡                                          (                                                                        5                          ⁢                                                      R                            5                                                                          -                                                  4                          ⁢                                                      R                            3                                                                                              )                                                        ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          3                      ⁢                      A                                        )                                                  +                                                      D                    22                                    ⁢                                      R                    5                                    ⁢                  sin                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          5                      ⁢                      A                                        )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    D                    23                                    ⁢                                      R                    6                                    ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          6                      ⁢                      A                                        )                                                  +                                                                            D                      24                                        ⁡                                          (                                                                        6                          ⁢                                                      R                            6                                                                          -                                                  5                          ⁢                                                      R                            4                                                                                              )                                                        ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          4                      ⁢                      A                                        )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      25                                        ⁡                                          (                                                                        15                          ⁢                                                      R                            6                                                                          -                                                  20                          ⁢                                                      R                            4                                                                          +                                                  6                          ⁢                                                      R                            2                                                                                              )                                                        ⁢                  cos                  ⁢                                      xe2x80x83                                    ⁢                                      (                                          2                      ⁢                      A                                        )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    D                    26                                    ⁡                                      (                                                                  20                        ⁢                                                  R                          6                                                                    -                                              30                        ⁢                                                  R                          4                                                                    +                                              12                        ⁢                                                  R                          2                                                                    -                      1                                        )                                                  +                                                      D                    27                                    (                                                            15                      ⁢                                              R                        6                                                              -                                          20                      ⁢                                              R                        4                                                              +                                                                                                                                                                                xe2x80x83                                    ⁢                                      6                    ⁢                                          R                      2                                                        )                                ⁢                sin                ⁢                                  xe2x80x83                                ⁢                                  (                                      2                    ⁢                    A                                    )                                            +                                                                    D                    28                                    ⁡                                      (                                                                  6                        ⁢                                                  R                          6                                                                    -                                              5                        ⁢                                                  R                          4                                                                                      )                                                  ⁢                sin                ⁢                                  xe2x80x83                                ⁢                                  (                                      4                    ⁢                    A                                    )                                            +                                                                                          xe2x80x83                            ⁢                                                D                  29                                ⁢                                  R                  6                                ⁢                sin                ⁢                                  xe2x80x83                                ⁢                                  (                                      6                    ⁢                    A                                    )                                                                                        (        b        )            
where Dm (m is an integer of 2 or higher) are coefficients.
It should be noted that to design an optical system symmetric with respect to the X-axis direction, D4, D5, D6, D10, D11, D12, D13, D14, D20, D21, D22 . . . should be used.
The above defining equations are shown to exemplify surfaces with a rotationally asymmetric curved surface configuration. Therefore, the same advantageous effects can be obtained for any other defining equation that expresses such a rotationally asymmetric curved surface configuration.
It should be noted that other examples of defining equations for free-form surfaces include the following defining equation (c):
Z=xcexa3xcexa3CnmXY
Assuming that k=7 (polynomial of degree 7), for example, a free-form surface is expressed by an expanded form of the above equation as follows:                                                         Z              =                              xe2x80x83                            ⁢                                                C                  2                                +                                                      C                    3                                    ⁢                  Y                                +                                                      C                    4                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                      C                    5                                    ⁢                                      Y                    2                                                  +                                                      C                    6                                    ⁢                  Y                  ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                      C                    7                                    ⁢                                      X                    2                                                  +                                                      C                    8                                    ⁢                                      Y                    3                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    9                                    ⁢                                      Y                    2                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                      C                    10                                    ⁢                                      YX                    2                                                  +                                                      C                    11                                    ⁢                                      "LeftBracketingBar"                                          X                      3                                        "RightBracketingBar"                                                  +                                                      C                    12                                    ⁢                                      Y                    4                                                  +                                                      C                    13                                    ⁢                                      Y                    3                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    14                                    ⁢                                      Y                    2                                    ⁢                                      X                    2                                                  +                                                      C                    15                                    ⁢                  Y                  ⁢                                      "LeftBracketingBar"                                          X                      3                                        "RightBracketingBar"                                                  +                                                      C                    16                                    ⁢                                      X                    4                                                  +                                                      C                    17                                    ⁢                                      Y                    5                                                  +                                                      C                    18                                    ⁢                                      Y                    4                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    19                                    ⁢                                      Y                    3                                    ⁢                                      X                    2                                                  +                                                      C                    20                                    ⁢                                      Y                    2                                    ⁢                                      "LeftBracketingBar"                                          X                      3                                        "RightBracketingBar"                                                  +                                                      C                    21                                    ⁢                                      YX                    4                                                  +                                                      C                    22                                    ⁢                                      "LeftBracketingBar"                                          X                      5                                        "RightBracketingBar"                                                  +                                                      C                    23                                    ⁢                                      Y                    6                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    24                                    ⁢                                      Y                    5                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                      C                    25                                    ⁢                                      Y                    4                                    ⁢                                      X                    2                                                  +                                                      C                    26                                    ⁢                                      Y                    3                                    ⁢                                      "LeftBracketingBar"                                          X                      3                                        "RightBracketingBar"                                                  +                                                      C                    27                                    ⁢                                      Y                    2                                    ⁢                                      X                    4                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    28                                    ⁢                  Y                  ⁢                                      "LeftBracketingBar"                                          X                      5                                        "RightBracketingBar"                                                  +                                                      C                    29                                    ⁢                                      X                    6                                                  +                                                      C                    30                                    ⁢                                      Y                    7                                                  +                                                      C                    31                                    ⁢                                      Y                    6                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                      C                    32                                    ⁢                                      Y                    5                                    ⁢                                      X                    2                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    33                                    ⁢                                      Y                    4                                    ⁢                                      "LeftBracketingBar"                                          X                      3                                        "RightBracketingBar"                                                  +                                                      C                    34                                    ⁢                                      Y                    3                                    ⁢                                      X                    4                                                  +                                                      C                    35                                    ⁢                                      Y                    2                                    ⁢                                      "LeftBracketingBar"                                          X                      5                                        "RightBracketingBar"                                                  +                                                      C                    36                                    ⁢                                      YX                    6                                                  +                                                      C                    37                                    ⁢                                      "LeftBracketingBar"                                          X                      7                                        "RightBracketingBar"                                                                                                          (        c        )            
It should be noted that an anamorphic surface or a toric surface is also usable as a surface having a rotationally asymmetric curved surface configuration.
Referring to FIG. 1 again, the optical path distributing part 20 has at least one pair of reflecting surfaces for left and right optical paths (i.e. a pair of back-coated mirrors 22L and 22R and another pair of back-coated mirror 23L and 23R in the case of FIG. 1). These reflecting surfaces are formed from rotationally asymmetric curved reflecting surfaces having the function of correcting decentration aberrations.
The point of the image display apparatus having a three-dimensionally decentered optical path according to the present invention is as follows.
The left and right optical paths (for the left and right eyes) of the viewing optical system are formed by optical surfaces 11L to 14L, 21L to 23L, 24, 11R to 14R, 21R to 23R and 24 arranged so that the left and right optical paths are not in plane symmetry with each other but in 180-degree rotational symmetry with respect to only a normal line A-Axe2x80x2 passing through the center of the image display device 3. In Example 1, the refracting surface (entrance surface) 24 through which the image light beam first enters the optical path distributing prism 20 from the image display device 3 is a surface common to the left and right optical paths.
To form left and right optical paths that are in 180-degree rotational symmetry with each other as stated above, the decentered prisms 10L, 10R and 20 should be arranged as follows. Pairs of optical surfaces (left and right) 11L, 11R; 12L, 12R; 13L, 13R; 14L, 14R; 21L, 21R; 22L, 22R; and 23L, 23R; are arranged and the surface 24 common to the left and right optical paths is formed so that when the optical surfaces 11R to 14R, 21R to 23R and 24, which constitute the optical system for the right optical path, are rotated through 180 degrees about the normal line A-Axe2x80x2, these surfaces are coincident with the optical surfaces 11L to 14L, 21L to 23L and 24, which constitute the optical system for the left optical path.
It is desirable that the optical path distributing part 20 should have at least two pairs of reflecting surfaces (left and right) 22L, 22R; and 23L, 23R; and the two pairs of reflecting surfaces should have rotationally asymmetric curved reflecting surfaces having the function of correcting decentration aberrations, as in the case of the example shown in FIG. 1.
Further, the left and right optical paths for the left and right eyes should desirably be arranged so that a plane defined by the optical axis of the axial principal ray incident on the left first reflecting surface 23L closest to the image display device 3 among the left reflecting surfaces in the left optical path of the optical path distributing part 20 and the axial principal ray exiting the left first reflecting surface 23L is not identical with a plane defined by the optical axis of the axial principal ray incident on the right first reflecting surface 23R closest to the image display device 3 among the right reflecting surfaces in the right optical path of the optical path distributing part 20 and the axial principal ray exiting the right first reflecting surface 23R.
If the left and right optical paths for the left and right eyes are not arranged as stated above, the left and right first reflecting surfaces 23L and 23R undesirably interfere with each other. Accordingly, it actually becomes difficult to form left and right optical paths for leading a light beam from the single image display device 3 to the left and right eyes.
Further, it is desirable that the left first reflecting surface 23L closest to the image display device 3 among the reflecting surfaces in the left optical path of the optical path distributing part 20 and the right first reflecting surface 23R closest to the image display device 3 among the reflecting surfaces in the right optical path of the optical path distributing part 20 should be positioned to face the image display device 3 and should be disposed adjacent to each other in a direction [i.e. the X-direction, which is the vertical direction in part (b) of FIG. 1] perpendicular to a plane [i.e. the YZ-plane in part (a) of FIG. 1] containing the centers of the exit pupils 1L and 1R of the left and right optical paths of the viewing optical system and also containing the center of the image display device 3.
In this case, it is desirable that an anti-reflection member should be provided for an area including the boundary portion between the left first reflecting surface 23L and the right first reflecting surface 23R to prevent light rays emitted perpendicularly (in the Z-direction) from the central region of the image display device 3 from being reflected as ghost light, as will be described later.
It should be noted that the viewing optical system, which comprises the ocular parts 10L and 10R and the optical path distributing part 20 as stated above, may be formed from a combination of reflecting mirrors (in Example 5, only the optical path distributing part 20 is formed from a combination of reflecting mirrors). However, the viewing optical system may also be formed from a single prism member [corresponding to Example 4 (described later)] or a plurality of prism members [corresponding to Examples 1 to 3 and 6 (described later); in Example 5, only the ocular parts 10L and 10R are prism members]. In such a case, all of the reflecting surfaces may be back-coated reflecting surfaces formed on the surfaces of the prism members.
The viewing optical system may also be arranged to include, as shown in FIG. 1, an optical path distributing prism 20 constituting the optical path distributing part, and a combination of a left ocular prism 10L constituting the left ocular part and a right ocular prism 10R constituting the right ocular part. The left ocular prism 10L and the right ocular prism 10R are separated from the optical path distributing prism 20 by an air space.
In this case, the optical path distributing prism 20 may include at least the following surfaces. That is, as in the case of the example shown in FIG. 1, an entrance surface 24 is disposed to face the image display device 3 so that both an image light beam forming the left optical path for the left eye and an image light beam forming the right optical path for the right eye enter the optical path distributing prism 20 through the entrance surface 24. The optical path distributing prism 20 further includes a left exit surface 21L through which the light beam of the left optical path exits the optical path distributing prism 20. At least two left reflecting surfaces 23L and 22L are disposed in the optical path between the entrance surface 24 and the left exit surface 21L to reflect the light beam of the left optical path within the optical path distributing prism 20. The optical path distributing prism 20 further includes a right exit surface 21R through which the light beam of the right optical path exits the optical path distributing prism 20. At least two right reflecting surfaces 23R and 22R are disposed in the optical path between the entrance surface 24 and the right exit surface 21R to reflect the light beam of the right optical path within the optical path distributing prism 20. The reflecting surface 23L closest to the entrance surface 24 in the left optical path and the reflecting surface 23R closest to the entrance surface 24 in the right optical path are positioned so as to face both the image display device 3 and the entrance surface 24. Moreover, the reflecting surfaces 23L and 23R are disposed adjacent to each other in a direction [i.e. the X-direction, which is the vertical direction in part (b) of FIG. 1] perpendicular to a plane [i.e. the YZ-plane in part (a) of FIG. 1] containing the centers of the exit pupils 1L and 1R of the left and right optical paths of the viewing optical system and also containing the center of the image display device 3.
Further, it is desirable that a distributed light reinforcing member should be disposed between the image display device and the optical path distributing part so that the light intensity of an image light beam emitted at a predetermined exit angle from each pixel located at least in the central portion of the single image display device is made higher by the distributed light reinforcing member than the intensity of a light beam emitted in a direction perpendicular to the display surface of the image display device.
As shown in FIG. 1, the left and right ocular prisms 10L and 10R may be prisms 10 (suffixes xe2x80x9cLxe2x80x9d and xe2x80x9cRxe2x80x9d for distinction between left- and right-side constituent elements are omitted) each having a first surface 14, a second surface 12, and a third surface 11 (13). The first surface 14 is an entrance surface through which a light beam exiting the optical path distributing prism 20 enters the prism 10. The second surface 12 is a reflecting surface for reflecting the light beam entering through the first surface 14 and totally reflected from the third surface 11 (13) within the prism 10 so that the light beam reflected from the second surface 12 is incident on the third surface 11 (13) at an angle smaller than the total reflection critical angle. The third surface 11 (13) is arranged so that the light beam entering the prism 10 through the first surface 14 is incident on the third surface 11 (13) at an angle not smaller than the total reflection critical angle so as to be totally reflected therefrom, and, at the same time, the third surface 11 (13) is an exit surface through which the light beam reflected from the second surface 12 exits the prism 10. This configuration of the prism 10 corresponds to Examples 1 to 3 and 5 (described later).
In this case, the first surface 14 of each of the left and right ocular prisms 10L and 10R may be formed with a rotationally asymmetric curved surface configuration that corrects decentration aberrations. The second surface 12 may also be formed with a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
In this case, it is desirable to arrange the left and right ocular prisms 10L and 10R so that the left axial principal ray exiting the optical path distributing prism 20 intersects, at a desired angle, a plane defined by the left axial principal ray exiting the left ocular prism 10L and the right axial principal ray exiting the right ocular prism 10R.
The left and right ocular prisms 10L and 10R may also be arranged as follows. As shown in Example 6 (described later), the left ocular prism is a prism having first to fourth surfaces. The first surface is an entrance surface through which a light beam exiting the optical path distributing prism enters the prism. The second surface is a reflecting surface for reflecting the light beam entering the prism through the first surface. The third surface is a reflecting surface for reflecting the reflected light beam from the second surface within the prism. The fourth surface is an exit surface through which the light beam reflected from the third surface exits the prism. The right ocular prism is a prism having first to fourth surfaces. The first surface is an entrance surface through which a light beam exiting the optical path distributing prism enters the prism. The second surface is a reflecting surface for reflecting the light beam entering the prism through the first surface. The third surface is a reflecting surface for reflecting the reflected light beam from the second surface within the prism. The fourth surface is an exit surface through which the light beam reflected from the third surface exits the prism. When the optical paths in the left and right ocular prisms are projected onto a plane containing the centers of the exit pupils of the left and right optical paths of the viewing optical system and also containing the center of the image display device, the optical path in each of the ocular prisms rotates within the prism in such a manner as to intersect itself.
In this case, the second surface of each of the left and right ocular prisms may be formed with a rotationally asymmetric curved surface configuration that corrects decentration aberrations. The third surface may also be formed with a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
In this case, it is desirable to arrange the left and right ocular prisms so that the left axial principal ray and the right axial principal ray exiting the optical path distributing prism intersect, at a desired angle, a plane defined by the left axial principal ray exiting the left ocular prism and the right axial principal ray exiting the right ocular prism.
In the foregoing arrangement, it is desirable that the viewing optical system should form an intermediate image of the image displayed by the image display device in the right optical path and also form an intermediate image of the image displayed by the image display device in the left optical path.
The image display device may be rotated through a desired angle about the normal line passing through the center of the image display device as an axis of rotation so that the horizontal direction of the image display area of the image display device is at an angle to a plane containing the centers of the exit pupils of the left and right optical paths of the viewing optical system and also containing the center of the image display device.
In the viewing optical system of the present invention, the surface configuration of each surface of the left and right optical systems is determined so that the optical paths for the left and right eyes are in 180-degree rotational symmetry with respect to only the normal line A-Axe2x80x2 passing through the center of the image display device 3, as has been stated above. Accordingly, the left optical system extending from the entrance surface 24 of the optical path distributing part 20 to the exit surface 11L of the left ocular part 10L and the right optical system extending from the entrance surface 24 of the optical path distributing part 20 to the exit surface 11R of the right ocular part 10R are in 180-degree rotational symmetry about the normal line A-Axe2x80x2. Moreover, the left and right optical systems are three-dimensionally decentered reflecting optical systems. Therefore, the relay image (intermediate image) of the image displayed by the image display device 3 is generally rotated through the same angle in the same direction about each optical axis. Accordingly, an image naturally oriented with respect to both the horizontal and vertical directions cannot be observed unless the image display device 3 is rotated in the opposite direction to the direction of rotation of the relay image (intermediate image) through the same angle as the angle of rotation about the normal line A-Axe2x80x2 as an axis of rotation so that the horizontal direction of the image display area of the image display device 3 is at an angle to a plane containing the centers of the exit pupils 1L and 1R of the left and right optical paths of the viewing optical system and also containing the center of the image display device 3.
Incidentally, it is desirable to satisfy the following condition:
10xc2x0 less than xcex8 less than 120xc2x0xe2x80x83xe2x80x83(1)
where xcex8 is the angle formed between the axial principal rays 2L and 2R of left and right light beams led from each pixel located at least in the central portion of the image display device 3 to the left and right eyes of the observer.
The condition (1) needs to be satisfied in order to separate the image light beams for the two eyes appropriately. If xcex8 is not larger than the lower limit, i.e. 10xc2x0, the effective diameter portions of the left and right optical surfaces, particularly those of the left and right first reflecting surfaces 23L and 23R closest to the image display device 3 undesirably overlap each other. Accordingly, the optical system has to be increased in size in order to ensure the required effective diameter of each of the left and right first reflecting surfaces 23L and 23R and hence becomes unsuitable for use as the optical system of a head- or face-mounted image display apparatus. Conversely, if xcex8 is not smaller than the upper limit, i.e. 120xc2x0, an image display device having very wide viewing angle characteristics is needed to serve as the image display device 3. At the same time, the solid angle of the image light beam becomes small. As a result, it becomes impossible to observe a bright image. Regarding the angle xcex8, it is preferable to satisfy the following condition:
15xc2x0 less than xcex8 less than 100xc2x0xe2x80x83xe2x80x83(1-1)
The above-described image display apparatus can be used as an image pickup apparatus in which an image pickup device is provided in place of the image display device 3 in the above-described arrangement. In this case, the exit pupils 1L and 1R are arranged as entrance pupils through which a light beam from a subject passes, and a subject image is formed on the image pickup device.
Further, the image display apparatus can be used as a projection apparatus in which a projection object is provided in place of the image display device 3 in the foregoing arrangement. A screen is placed in front of the exit pupils 1L and 1R to form a projected image of the projection object on the screen.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.